Batteries are known devices that are used to store and release electrical energy for a variety of uses. In order to produce electrical energy, batteries typically convert chemical energy directly into electrical energy. Generally, a single battery includes one or more galvanic cells, wherein each of the cells is made of two half-cells that are electrically isolated except through an external circuit. During discharge, electrochemical reduction occurs at the cell's positive electrode (sometimes referred to as the cathode), while electrochemical oxidation occurs at the cell's negative electrode (sometimes referred to as the anode). While the positive electrode and the negative electrode in the cell do not physically touch each other, they are generally chemically connected by at least one (or more) ionically conductive and electrically insulative electrolyte(s), which can either be in a solid or a liquid state, or in combination. When an external circuit, or a load, is connected to a terminal that is connected to the negative electrode and to a terminal that is connected to the positive electrode, the battery drives electrons through the external circuit, while ions migrate through the electrolyte.
Batteries can be classified in a variety of manners. For example, batteries that are completely discharged only once are often referred to as primary batteries or primary cells. In contrast, batteries that can be discharged and recharged more than once are often referred to as secondary batteries or secondary cells. The ability of a cell or battery to be charged and discharged multiple times depends on the Faradaic efficiency of each charge and discharge cycle.
While rechargeable batteries based on alkali metals (lithium and sodium) can comprise a variety of materials and designs, almost all cell designs electrode solutions in the cell are able to intermix over time and, thereby, cause a drop in Faradaic efficiency and loss of battery capacity. This is true of conventional lithium ion batteries that typically utilize a polymeric separator having a thickness of about 2 to 3 microns. Sometimes the polymeric separators are combined with a thin (less than 1 micron) ceramic coating.
The thin separator enables high current density applications, but lacks the self-supporting integrity to maintain separation of the chemical contents of the positive and negative electrodes in the event of separator failure. Separator failure is known to occur when the battery overheats and causes the polymeric separator to melt. Such separator failure has occurred with lithium ion batteries, causing catastrophic fire and explosion.
Thus, while alkali metal rechargeable batteries are available, challenges with such batteries also exist, including those mentioned above. Accordingly, it would be an improvement in the art to provide an alternative separator for alkali metal ion batteries that will provide enhanced battery safety.